ack Sarfatti
Paul Zielinski report on time travel to the past
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  • Jack Sarfatti CTC = Closed Timelike Curves allows in principle time travel to the past as in some UFO evidence.

    On Jun 7, 2013, at 3:46 PM, Paul Zelinsky <This email address is being protected from spambots. You need JavaScript enabled to view it.> wrote:


    Here is the review of CTCs I did for Dan. Let me know what you think.


    -------- Original Message --------
    Subject: Re: CTCs.....
    Date: Tue, 04 Jun 2013 12:13:50 -0700
    From: Paul Zielinski <This email address is being protected from spambots. You need JavaScript enabled to view it.>
    Reply-To: This email address is being protected from spambots. You need JavaScript enabled to view it.
    To: Dan <This email address is being protected from spambots. You need JavaScript enabled to view it.>
    CC: David Gladstone <This email address is being protected from spambots. You need JavaScript enabled to view it.>

    Hi Dan,

    OK I've done my technical review of CTCs and here is a summary of my take on this. I won't copy Jack on this until we've had a chance to talk about it.

    Here goes:

    1. CTCs are a feature of numerous spacetimes with metrics that are mathematically well behaved and are fully compatible
    with the principles of classical GR.


    Well known examples include

    => The Godel universe: Rev. Mod. Phys. 21 (3): 447–450 (1949)
    => Van Stockum spacetimes: van Stockum, WJ, Proc. R. Soc. Edin. 57, 135–154 (1937)
    => Tipler cylinders: Tipler FJ, Phys. Rev. D9, 2203–2206 (1974)
    => Longitudinally spinning cosmic strings: Visser M. (1995).
    => Kerr and Kerr–Newman geometries: Hawking and Ellis, The Large Scale Structure of Spacetime (1973)
    => Gott’s time machines: Gott JR, Phys. Rev. Lett. 66, 1126-1129 (1991)
    => Wheeler wormholes (spacetime foam): Wheeler JA, Geometrodynamics (1962)
    => Morris–Thorne traversable wormholes: Morris MS and Thorne KS, Am. J. Phys. 56, 395–412 (1988).
    => Alcubierre “warp drive” spacetimes: Alcubierre M, Class. Quant. Grav. 11, L73–L77 (1994)


    2. Paradoxes allegedly associated with such CTCs, namely the grandfather paradox and the self-causality paradox, were
    initially thought to exclude CTCs and GR time machines as unphysical, leading to Hawking's "chronology protection conjecture"
    (CPC) which barred all GR metrics featuring CTCs (Hawking SW, Phys. Rev. D46, 603-611 (1992)). The divergences predicted
    to occur at chronology horizons in such universes in the context of classical GR (Hawking SW, Ellis GFR: The large scale
    structure of space-time (1973)) which would prevent CTCs from forming were later found not to occur in the context of quantum
    gravity (e.g., Kim SW, Thorne KS, Phys. Rev. D43, 3929 (1991)).


    3. In the 1970s and 1980s Igor Novikov discussed the possibility of CTCs in the context of classical GR, and then later
    co-authored a paper on the subject (Friedman, Novikov, et al, Phys. Rev. D, 42 (6). pp. 1915-1930 (1990)) in which
    the following self-consistency conditions for physical CTCs was proposed:

    "The only solutions to the laws of physics that can occur locally in the real Universe are those which are globally self-

    The authors of the 1990 Phys. Rev. paper remarked,

    "This principle allows one to build a local solution to the equations of physics only if that local solution can be extended to a
    part of a (not necessarily unique) global solution, which is well defined throughout the non-singular regions of the spacetime."


    3. Further research, reviewed for example by Kip Thorne et al. (Morris MS, Thorne KS, and Yurtsever U, Phys. Rev.
    Lett. 61(13) 1446-1449 (1988)) and later by Matt Visser (Visser M, “The Quantum Physics of Chronology Protection” (2003)) led to
    the conclusion that Hawking's CPC is not an essential feature of classical GR, and that definitive answers to the question of the
    physical admissibility of CTCs would have to await a deeper and more complete understanding of quantum gravity.


    4. In a seminal 1991 paper David Deutsch (Phys. Rev. D 44(10): 3197–3217 (1991)) explored the implications of CTCs in the
    context of quantum computational theory, and proposed a self-consistency condition on the density matrices of CTC qubits that he
    claims resolves the grandfather paradox (although not everyone accepts Deutsch's arguments). Deutsch’s self-consistency condition
    essentially requires that the density matrix of the CTC system after an interaction be equal to the density matrix before the interaction.
    Deutsch tacitly assumes a spacetime in which CTCs exists and applies QM to the CTC forward-in-time and backwards-in-time
    information transfers and concludes that quantum phenomena observable near such trajectories at the macroscopic level ensure
    that the grandfather paradox is resolved and the proposed consistency condition is satisfied.

  • Jack Sarfatti In his 1991 paper Deutsch said:

    "I have shown that the traditional 'paradoxes' of chronology violation, whatever position one takes on their seriousness, do not
    occur at all under quantum mechanics."

    "The physics near closed timelike lines is dominated by macroscopic quantum effects and has many novel features. The
    correspondence principle is violated. Pure states evolve into mixed states. The dynamical evolution is not unitary nor is it even
    the restriction to a subsystem of unitary evolution in a larger system."

    "All these effects are stable and do not require the maintenance of quantum coherence. They therefore apply to macroscopic

    5. In 2009 G. Svetlichny proposed ("Effective Time Travel", arXiv:0902.4898v1 [quant-ph] (2009)) that a quantum teleportation
    protocol can be used to simulate a physical CTC, arguing that the probabilistic nature of the QM predictions resolves all paradoxes
    associated with CTCs. Such a time loop is described as the "QM analog of a CTC". However, since this is a QM teleportation
    model, in such models only the qubit content of the state of the teleported entangled system is sent back into the past, as opposed
    to the entangled system itself:

    "What we have... is effective time travel. After the fact of the measurement M taken place there is no empirical way to falsify
    the statement that the qubit at A did travel back in time to B, but this is not true time travel. By true time travel I mean one whose
    denial can be falsified by empirical evidence. One can however ask if any of the supposed effects and benefits of supposed
    true time travel do somehow exist in this case. The surprising answer is yes, but obviously those that cannot lead to time travel
    paradoxes. In these cases, time travel is a reading of the situation which can otherwise be analyzed in usual quantum
    mechanical terms."

    Essentially the quantum circuit with the back-in-time channel is treated as a metaphor for a physical CTC that allows certain
    conclusions to be drawn about their behavior and to show how time travel paradoxes can be resolved:

    "Of course the above is a narrative and should not be simply accepted as a description of a physical process. All philosophically
    or scientifically motivated discussions of time travel have been likewise narratives as the time travel process, or time machine, is
    necessarily merely hypothesized to have certain properties not being able to refer to physically realizable situations. This type of
    narrative is at best a meta-theoretic discussion, for instance exploring the question as to whether the existence of supposed true
    time travel is consistent with present physical laws or do these need to be modified to admit it. In our narratives neither the claim
    nor the denial of time travel can be empirically falsified. This non-falsifiability makes both the claim and the denial non-scientific
    assertions. On the other hand our narrative takes place in the context of a physically realizable process and so cannot lead to
    any contradiction. We thus have a source of time travel narratives in which all paradoxes are resolved and this has interesting
    philosophical and scientific implications." - p5
  • Jack Sarfatti 6. In 2010 Seth Lloyd et al., following the same basic approach as Svetlichny, published two papers in which they proposed the
    use of post- selected quantum teleportation protocol to simulate a physical CTC, with a self-consistency condition
    different from Deutsch's that has different physical consequences ("P-CTC"). Lloyd et al.'s P-CTC protocol operates by combining
    a chronology-respecting qubit with a chronology-violating qubit, and allowing them to interact under unitary evolution. After such
    interaction, the chronology-respecting qubit goes forward in time, while the chronology-violating qubit goes back in time. It is
    assumed that the unitary evolution of the 2-qubit system is mathematically equivalent to combining the state of the chronology-
    respecting qubit with a maximally entangled Bell state. There follows a unitary interaction between the chronology-respecting
    qubit and half of the entangled Bell state. The final steps in the protocol are the projection of the two substates onto the entangled
    Bell state, then non-linear renormalization of the state, followed by tracing out of the last two systems.

    As mentioned above, Deutsch’s self-consistency condition requires that after unitary interaction the density matrices of the CTC
    system before and after the interaction are equal. This was designed to reproduce the predictions of ordinary QM without CTCs.
    Post-selected CTCs, on the other hand, are effectively equivalent in this approach to “post-selection with certainty”, which the
    authors argue neatly excludes all unitary evolutions resulting in paradoxes.

    7. The thermodynamic implications of CTCs, and thermodynamic arguments for and against chronology protection, are explored
    by Michael Devin (Devin M: Thermodynamics of Time Machines (2013)). No conclusive argument against CTCs is evident in this
    Devins' paper.


    Hawking SW, Phys. Rev. D 46, 603-611 (1992)

    Thorne K: Closed Timelike Curves (1993)

    Visser M: The quantum physics of chronology protection (2002)

    Roberts B: Closed Timelike Curves (2008)

    Morris et al: Wormholes. Time Machines, and the Weak Energy Condition (1988)

    Deutsch D: Quantum mechanics near closed timelike lines, Phys Rev D 44(10), 3197–3217 (1991)

    Svetlichny G: Effective Quantum Time Travel (2009)

    Lloyd S et al: Closed timelike curves via post-selection: theory and experimental demonstration (2010)

    Lloyd S et al: The quantum mechanics of time travel through post-selected teleportation (2010)


    So from the standpoint of physics, what is the bottom line for CTCs? From the above it appears that CTCs are not only a feature
    of numerous mathematically well-behaved spacetimes that are compatible with classical GR, but the feared time-travel paradoxes
    associated with CTCs in the context of classical or semi-classical GR can be resolved by the use of quantum computational protocols
    to model the forward-in-time and back-in-time qubit information transfers that can be expected to occur in such loops, even if the QM
    protocols are really only metaphors (models) in relation to actual physical CTCs that are associated with certain solutions of the GR
    field equations. Thus far from enforcing Hawking's CPC, these protocols appear to make it irrelevant. Which I suppose is good news
    for you.

    What is not so good news for you is that both the Deutsch and Seth Lloyd et al. approaches piggyback on classical CTCs. They
    both *presuppose* the existence of spacetime CTCs, and investigate the time travel paradoxes associated with then using quantum
    computational techniques. The only difference between Deutsch and Lloyd et al. consists in application of different quantum
    informational self-consistency principles with different physical consequences, which in the case of Lloyd et al. is based on a post-
    selected quantum teleportation model. This means that CTCs are still a feature of certain 4D spacetimes, and are thus not buried in
    any quantum "implicate order". Both Deutsch and Lloyd et al. use QM to see how the information transfer properties of classically
    defined CTCs play out in the context of QM.

    Thus the relationship between CTCs and the holographic universe is much the same as any other world line -- CTCs belong to the
    "explicate" order. So if only the explicate order is to be regarded as fundamental, such CTCs cannot be regarded as fundamental.
    The belong to the explicate physical reality that may or may not be encoded on a 3D hypersurface according to the holographic


    Now as to the relevance of CTCs to your BPWH, there is a tricky question of interpretation. The standard interpretation of physical
    CTCs wherein a particle moving along a CTC can return to an earlier time to "bump into itself" seems questionable, since there is
    nothing in the principles of GR to suggest that the mere existence of such a closed timelike trajectory must convert one object into
    two. It seems arguable to me that an alternative interpretation in which the returning object is one and the same as the starting object,
    and experiences endless recurrences of its life history along the CTC, is a more natural one. But then one has to deal with the
    internal properties of the object and irreversible thermodynamic processes and how they relate to the proper time intervals around
    the CTC.

    I disagree here. There will be two copies and older and a younger. This is what Deutsch says and I agree with Deutsch.

    You said that you would like to insert a "spark gap" into such a CTC, that would somehow be analogous to a Wheelerian self-excited
    loop. The only solution I have been able to think of so far is a wormhole with its mouth positioned along the CTC. This might create a
    "gap" without actually interrupting the CTC. But I'd like to hear more from you about exactly you are looking for before pursuing this

    As I see it the next step in this project is to investigate the meaning of black hole thermodynamics (as per Beckenstein) and the
    holographic model for the universe, and there implications for your BPWH metaphysics.

    S. W. HawkingDepartment of Applied Mathematics and Theoretical Physics, University of Cambridge, Silver Street, Cambridge CB3 9EW, United Kingdom